In an enclosure containing electrical apparatus, it is often desirable to have the incoming electric service lines first connect to an isolation switch, and then other electrical apparatus to attach to the downstream side of the isolation switch. Often fuses, circuit breakers or other overload interrupt devices are attached downstream from the isolation switch.
It is desirable to have an overload blow a fuse or trip a circuit breaker rather than blow open the isolation switch. Fuses and circuit breakers are designed to interrupt the heavy currents to be expected during short circuit conditions. An isolation switch is not designed to interrupt such heavy current flows. However, electromagnetic forces generated during high current conditions experienced during a short circuit may generate forces on the conductors of the isolation switch and the isolation switchblades. The forces may be of such a nature as to drive the switchblades "open". Thus, under heavy current flow short circuit current conditions, the isolation switch may be blown open by the current flowing through the switchblades. The purpose of the isolation switch may thereby be defeated by the electromagnetic forces generated during short circuit conditions, and the fuse or other interrupt device may not have an opportunity to interrupt the circuit because the isolation switch is blown open.
A continuing problem in the design of isolation switches has been to develop a system which will withstand the electromagnetic forces generated during severe short circuit conditions.